However, I not clearly understand about RSemulator and the network configuration. I will try to explain my understanding, and would like to confirm with your guys.
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Here is what I think the allen bradley ethernet network setup in the real world:

First, If PLC A and PLC B are in different network both have ethernet module, to identify the network and node, IP address is all we need.

After both PLC has the Ethernet module configured in the IO tree. If PLC A produce tags, and PLC B consume tags, PLC B need to configure the PLC A ethernet module. In the PLC B IO tree, under the PLC B ethernet module, add another ethernet module with the PLC A ethernet module IP address.

Then, set up the consume tag, chose the correct producer.

We do not have to use other software, unless the PLC in different network, and different protocol, like Ethernet to DeviceNet. Then DeviceNet configuration is needed.
Do we need RSNetWorx setup?
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Here is my understanding on RSemulator:

The RSemulator only sending message to local. We can not emulate a ethernet module. Therefore we can not emulate a network, at least not through the etherent.

However, we still can use RSlinx gateway and third party software(kepware linkmaster). Setup OPC server for 2 emulated PLC in different machine, and manual establish OPC server connection tag by tag in the linkmaster.

RSemulator does not communicate to other RSemulator through any protocol(ethernet/devicenet)

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I think these are the cases, but I want to make sure with you pros, All these information are from my imagination, I grab the information piece by piece. I dont have a way to confirm my thought, besides with your references.

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Something besides PLC,
This is my first job after I graduate, and I am in this industry like almost 3 years, but boss did not teach me much, basely learn everything by myself. I start touch allen bradley last year, and I am struggling in "not sure what is correct", what is the right way to do. Mostly, I am confused with my progress. With 3 years experience, should know more than this, but I still feel like I know ****. With 3~4 years, you can get a PE license already...Meanwhile the new people come-in, I teach them as much as I can, so they definitely can catch-up much faster. But I still dont know much about process control, and only know superficial knowledge in PLC. I am lost.